You probably know the basics: Here's the whole story. If you are an average, healthy woman not taking a hormone-based contraceptive (and who hasn't yet reached menopause), each month, one of your two ovaries (paired, almond-sized organs located in your pelvis) most likely releases an egg into your Fallopian tube. The egg travels through this tube to your uterus (a small, hollow organ designed to house a developing fetus). If the egg is fertilized by sperm on the way, it imbeds itself in the uterine lining (which has become nice and thick, in case this happens) and you become pregnant.

If the egg is not fertilized, about two weeks after ovulation, the body sheds the unfertilized egg along with built-up layers of the uterine lining (endometrium). This discharged blood and tissue passes through the cervix (the neck of the uterus) into the vagina, and you get your menstrual period. The cycle then repeats--meaning, an ovary releases another egg about two weeks later.

Knowing Your Body
 
Your period is one of the most telling signs of your reproductive health.
Many Variations
That's the "simple" answer. Because we are each unique, you may experience differences from this description, most of which are typical and healthy. First of all, your cycle might not be exactly "monthly." The long and short of it is that while the average length of a menstrual cycle (first day of your period to first day of your next period) is about 28 days, this isn't true for every woman.

Preparing For The Big Event
The best way to understand why your cycle is the length it is, is to take a glimpse at what happens between each period. On the day you start bleeding, you begin the follicular phase of your cycle. Follicles (clusters of cells enclosing a developing egg) begin to grow inside the ovaries. Meanwhile, the endometrial cells begin to reproduce, thickening the uterine lining. Usually just one follicle fully matures and releases an egg--the big event the reproductive cycle is all about. The time from when your last period began and ovulation begins is about two weeks (14 days).

 
The follicular phase of your cycle begins on the first day of your last period, and ends at ovulation.
 

The second phase, the luteal phase, starts when the mature egg is released from the ovary. When this happens, the egg travels through the Fallopian tube. If the egg is fertilized by sperm, you become pregnant. If not, the egg dies (about 24 to 48 hours after being released) and about a week or two later, the unfertilized egg is released along with the external layers of the uterine lining in the form of a menstrual period. This second phase of the cycle lasts from ovulation to the onset of the next menstrual period, and is also about two weeks (14 more days) in length.

Finding Your Rhythm
Your pattern may be a bit different. For example, you may ovulate 10 days after the start of your period (making your follicular phase 10 days) and get your period 15 days after that (making your luteal phase 15 days)--meaning your cycle is 25 rather than 28 days. Your friend may ovulate 16 days after the start of her period and get her period 16 days after that--meaning her cycle is 32 days. Your follicular phase is more likely to change from month to month than your luteal phase. The length of your luteal phase (the time from ovulation to menstruation) tends to be consistent for each person.

The Rhythm of Life
Your body's schedule can change as well. Factors that can influence the length of your cycle include stress, exercise, change in diet, consumption of drugs or alcohol, or reasons you can't quite figure out. In other words, there is no one pattern that is "normal." Each woman has her own rhythms and it is very natural for one woman's schedule to vary slightly from cycle to cycle.

The Pill Prevents Ovulation
For most women taking birth control pills, the whole story is decidedly different because most Pills work by inhibiting ovulation. In other words, when taken as directed, most OCs prevent pregnancy by preventing ovulation.

Whether you are taking the Pill or not, hormones are a very important part of your reproductive health. Click here to learn more.

 
 
The luteal phase of your cycle lasts from ovulation to the first day of your next menstrual period.